Can there be several answers to an inference question?

There is usually just one.  Possible variations will all be created in the mind of the student.  The task of the assessor is to teach these students to read analytically and to answer with judgement.

There are 2 ways of knowing:
•  use ‘writer’s intent’ and common sense as a guide
•  use the key words in the Guide and Answers book

Writer’s intent means that the writer is directing the reader to a particular viewpoint or opinion. If the reader refers to something the writer has not alluded to then it cannot be included in their answer.  If you aren’t sure if your student is correct then ask them how they arrived at their answer.
If they are right, their explanation will include all or some of the given key words.
If they are wrong, their explanation will include words and information that are not derived from the text.

Can I bypass inference and go to evaluation?

This is not advisable.  It is always best to ensure that the skills of reorganisation and inference are well understood and used competently before embarking on evaluation. 

Evaluation is a combination of these two skills, and therefore requires more ‘reading between and beyond’ the lines. 
There are more questions that require an abstract answer in KEY into evaluation than there are in the other resources.  This can be difficult even for adult students.